1. Field of the Invention
The present invention relates to a data playback apparatus for and a data playback method of receiving data from, for example, a network and playing back the data.
2. Description of Related Art
When a conventional data playback apparatus receives packet data from, for example, a network, the data playback apparatus stores the packet data in a receive buffer, and, when the number of packet data stored in the receive buffer exceeds a reference value, the data playback apparatus starts a playback of the packet data stored in the receive buffer. After that, because a substantially constant amount of packet data is stored in the receive buffer, even if the number of packet data received temporarily decreases because of occurrence of a network fluctuation, the conventional data playback apparatus can perform a playback of packet data with stability while receiving packet data from the network because an extra amount of packet data is stored in the receive buffer.
Therefore, even if a transmission fluctuation occurs, the conventional data playback apparatus can continue to carry out a playback of packet data only during a time period during which a number of packets corresponding to the reference value are stored. Furthermore, when the conventional data playback apparatus detects decrease or increase in the number of packets stored in the receive buffer while playing back packet data for a long time, the conventional data playback apparatus can adjust the number of packets stored in the receive buffer by adjusting the playback speed of packet data (see patent reference 1).
However, the adjustment of the playback speed of the packet data on the basis of the number of packets stored in the receive buffer causes the time required for a predetermined number of packet data to be stored in the receive buffer to be not constant when packet data whose number per unit time is not constant are received, and therefore causes the degree of resistance to network fluctuations (the time period during which the data playback apparatus can withstand network fluctuations) to become unstable. In addition, in order to strengthen the resistance to network fluctuations, if the reference number of packets is increased too much, a time delay which occurs before the data playback apparatus starts a playback of packet data increases. For example, in a case in which the number of packets per unit time becomes unconstant if the reference number of packets is set to 100 packets, it takes 1 second to store packet data with 100 packets in the receive buffer at a time, or it takes 3 seconds to store packet data with 100 packets in the receive buffer at another time. Actually, this time period of 1 or 3 seconds is the degree of resistance to network fluctuations, and, when the fluctuation resistance of 1 second is sufficient, 3 seconds of delay can provide the user with displeasure at the time of real time communication.    [Patent reference 1] JP, 2001-45065,A (see paragraph numbers [0038] to [0042] and FIG. 1)
Because the conventional data playback apparatus is constructed as mentioned above, there is a problem that when packet data whose number per unit time is not constant are received, the time required for a predetermined number of packet data to be stored in the receive buffer becomes inconstant and therefore the degree of resistance to network fluctuations becomes unstable. Another problem is that when the reference number of packets is increased too much in order to strengthen the resistance to network fluctuations, a time delay which occurs before the data playback apparatus starts a playback of packet data increases.